Method of treating wood with an improved fire retardant composition



8, 1964 I. s. GOLDSTEIN ETAL 3,160,515

METHOD OF TREATING woon WITH AN IMPROVED FIRE RETARDANT COMPOSITION Filed Dec. 18, 1961 UNTREATED WOOD ORGANOPHOSPHORUS ESTER IMPREGNATING ORGANIC SOLVENT EVAPORATING ORGAN|C SOLVENT GASEOUS AMMONIA AMMONIATING DEGASSING UNREACTED AMMONIA FIRE RE TA RDANT WOOD INVENTORS IRVING S. GOLDSTEIN 8 WILLIAM J. OBERLEY The/r United States. Patent METHOD OF TREATING WOOD WITH AN IM- PROVED RETARDANT COMPOSITION Irving S. Goldstein, Pittsburgh, and William J. Oberley,

Pitcairn, Pa, assignors to Koppers Company, Inc, a

corporation of Delaware Filed Dec. 18, I961, Ser. No. 160,321 7 Claims. (Cl. 117-621) This invention relates to an improved method of treating wood with an organic fire retardant solution and the novel compounds produced thereby. In one specific aspect, it relates to an improved method of impregnating wood with an organic solvent-soluble fire retardant in an organic solution whereby the external dimensions of the wood remain unafiected by reacting the impregnated fire retardant. chemical in situ with gaseous ammonia.

In our copending application, S.N. 160,322, filed on even date herewith, we described and claimed a new method of treating wood with. \an organic fire retardant solution. This method involves treating wood with an organic solvent-soluble fire retardant in an organic solu tion without affecting the external dimensions of the wood by impregnating the wood under impregnating pressure and at a temperature below the boiling point of the organic solvent under said pressure, with a solution consisting of a diester of phosphorous or phosphoric acid and an organic solvent boiling below about 80 C. By impregnating with an organic solution, instead of an aqueous solution used heretofore, we have eliminated a major difiiculty which is inherent in treating wood with an aqueous medium, namely swelling and dimensional distortions of the wood produced during impregnation. Thus it is nowpossible to impregnate finished lumber, cut to size and shape, with fire retardant chemicals.

Quite surprisingly, we have discovered an improvement in the. method of impregnating wood with an organic solventrsoluble fire retardant which. produces enhanced fire retardance and also extends the scope of compounds producing effective results. This improvement involves reacting the organophosphorus compound in situ with gaseous ammonia.

It is, therefore, an object of the invention to provide an improved method oftreatingwood with a non-swelling fire retardant solution.

. It is another object of the invention toprovide a method of treating wood, impregnated with an organic solventsoluble fire retardant, with a non-swelling medium to produce enhanced fire retardance.

In accordance withour invention, wood is impregnated withla solution of an ester of phosphoric or phosphorous acid in an organic solvent having. a boiling point below about 80 C. under wood impregnating pressure at a temperature below the boiling point of the solvent under said pressure, and thereafter the organic solvent is removed from the impregnated wood. The organophosphorus ester within the impregnated solvent-free woodis then reacted under pressure with gaseous ammonia and the unreacted ammonia is removed.

The ammonium salts of org anophosphorus compounds A possiblegive improved fire retardant properties. theory is that when the wood is burned, the ammoniated salt is'broken down and decomposesto gaseous ammonia which dilutes the combustible gases to la non-combustible mixture. To impregnate the wood with the prepared annnoniated salts presents. a problem since although these compounds are soluble in water, they are insoluble in organic. solvents. We have now discovered a. method of reaping the advantage of the ammoniated compounds while avoiding the aqueous treatment by impregnating the. wood with the organophosphorus esters. in an organic solution and treating the impregnated wood with gaseous retained by the treated wood, in order to give satisfactory 3,160,515 Patented Dec. 8, 1964 ammonia whereby the salts are formed in situ. It is also possible to reverse the order of the operation so that the wood is first amnioniated and subsequently impregnated with the organophosphorus ester. These reactions may be exemplified by the following equations:

wherein R is lower alkyl or chlorinated lower alkyl and X is hydroxy.

Gaseous ammonia will react in the wood with organ cphosphorus esters, if small amounts of moisture are present in the wood. The moisture present in the wood usually is sutficient for the reaction to occur buta minimum of about 4 percent is required. The moisture content of dried lumber is considerably above the minimum requirement as shown by air-dried lumber which has a mimrnum moisture content ranging from 12 to 15 percent and kiln dried lumber of soft and hard Woods which has a minimum moisture content ranging from 6 to 12 percent. The reaction on a molar basis requires about one mole water for each mole of organophosphorus ester.

Compounds useful in our invention are certain organic diesters Olf phosphoric and phosphorous acid and trimethylphosphite. These compounds are diesters having the formula;

[0111-1 (ROhi X wherein R is member selected from the group consisting of lower alkyl and chlorinated lower alkyl, X is a hydroxy radical and n is an integer having a value of from one to two; and tri'rnethylphosphite. Particularly useful com pounds are: dimethy-l phosphite, diethyl phospln'te, diethyl phosphate, bis(beta-chloroethyl) phosphate, bis(1,3-dichloropnopyDpho-sphite, bis(1,3 dichloropropyDphosphate, and trimethyl phosphite.

The amount of ammoniated fiarne retardant chemical flame retardance, should be within a range of about 5 to 20 percent by weight of the dry wood. Less than 5 percent retention does not oiier sufiicient protection, whereas more than 20 percent retention is found unnecessary.

The concentration of solute in solution depends to a large extent on the void spaces in the particular Wood to be treated. The usual impregnating solution contains about 10 to 25 percent of the organic solvent soluble fire retardant material. For accurate determinations of the concentration of solute required to obtaineifective fire retardance, empirical determinations should be made by taking samples of the particularwood to be treated and determining the retention of the fire retardant in the wood.

impregnation of wood is conveniently accomplished by a full cell cycle. The object of the full cell process is to fill the structure of the wood with the treating solution. This is accomplished by subjecting the treating reactor containing the wood to be treated to a vacuum of about 22 to 26 inches of mercury for a period of time ranging from. about 15 minutesto an hour; The reactor is. then filled treating. solution and. subjected to a pressure of about 1 25 to 200 psi. at 25 to C. for about one and a half to three hours- The larger'and more. dense pieces of wood require either a; longer vacuum period, a longer pressure period or perhaps both. For most woods, a 15 minute vacuum of 25 to 26' inches of mercury followed by a two hour pressure process of psi. at ambient temperature is adequate.

Other standard impregnation techniques known. to the art can also be used taking into consideration, of course,

below about 80 C. so that they may be readily removed from the treated wood after impregnation. Solvents useful in our invention are the lower alltyl'chlorinated solvents such as chloroform, carbon tetrachloride and methylene chloride, ether, benzene and pentane. Miro tures of solvents are also useful in our invention such as benzene mixed with a liquid low boiling alkane such as pentane and hexane.

The maximum temperature at which impregnation is performed must of necessity vary with the solvent being used. Ambient temperatures are satisfactory. However,

the temperature cannot be so high that it will be above the boiling point of the solvent at the operating pressure. The pressure is not critical and wood impregnating pressure may be used such as using a pressure of up to However, on the basis of the above equations, one mole per mole of phosphite and acid' phosphate esters and two moles per mole of halophosphate esters is required. The time required for the ammonia treatment depends on numerous variables, such asthe type of Wood, the dimensions of the wood, and the pressure of the treatment. One method of determining whether the reaction has gone to completion is to insert a thermocouple into the wood, which since the reaction is exothermic, will show a temperature decrease when the reaction has terminated. A treatment of from one to three hours is generally 7 After the reaction has terminated," the unsufiicient. reacted gaseous ammonia is removed by diifusion at a pressure ranging from atmospheric to sub'atmospheric,

such as a vacuum up to 30 inches Hg. 7

The flame retardance of wood may be conveniently measured by the percentage weightless in the fireproof test. A standard test is the ASTM method 13-69-50.

Using this test, a fire-tube weight loss of approximately 40 percent is indicative of moderate fire retardance and I V d was placed in a cylinder and subjected to reduced pressure for 15 minutes. Dry ammonia gas was, thereafter, forced into the cylinder under a pressure of 12 p.s.i. for a period of 30 minutes, after which the excess ammonia was removed. by diffusion at atmospheric pressure. During the ammonia treatment, ammonium methyl phosphite was formed in situ' within" the'impregnated samples.

Both groups of samples were tested in a tire tubeapparatus according to the ASTM E-69-50 test method. A comparison between the non-ammoniated and ammoniated samples showed that: (l) dimethyl phosphite impregnated samples gave rapid and complete flame spread,

, and had a weight loss of 4-5 percent, and (2) dimethyl ph'osphite impregnated samples treated with ammonia gave no flame spread and had a weight loss of percent.

I Example II The'procedure of Example I was repeated using other compounds instead of dimethyl phosphite. The dried. samples retained approximately 15 percent by weight of the solute. Results are given in the following table:

r Per- Test Compound eevntt Flame Spread Loss A {Bis(betsrchloroethyl) phosphite- Slight.

' Bis(beta-chloroethyl)phosphite-t-NE 20 None.

Diethyl phosphiten"; 55 Fast and B complete.

Diethyl phosphite+NH 2S Slight. Diethyl phosphate 45 Fast and C I complete. Diethyl phosphate-l-NH 26 Slight.

Triethyl phosphite 72 Fast and D complete.

Trietbyl phosphite+NH 75 Do. Tris (dichloropropyl) p11 osphatefl; 73 Moderately E r a fast and Y I complete.

Tr1s(dieh1oropropyl)phospl1ate+NH 75 Do.

less than 30 percent is considered good. Injaddition, the

rate and extent of flame spread may be observed and estimated. I

examples: 7

Example I Twenty pieces of southern yellow pine, having the dimensions x x 40', were impregnated-at ambient V temperatures with a 15 percent solution, of dir'nethyl phosphite in benzene. Using the fullcell method, the

samples were placed in a treating cylinder under an initial vacuumof '27 inches Hg for 1 5' minutes'followed by a divided into two groups of ten pieces each. Que g oup Ourinvention is further illustrated by the following It was deter- Example 111 Y The procedure of Example I was repeated usingtrimethyl phosphite in a pentane solvent instead of dimethyl phosphite in a benzene solvent. The dried samples retained approximately 15 percent by weight of the solute. Results showed that: (1) trirnethyl phosphite impregnated samples gave rapid and complete flame spread and had'a weight loss of. 73 percent,,and (2) tr'imethyl phosphite impregnated samples treated with ammoniagave slight flame spread and had a weight loss of 30 percent.

Weclairn: l. A method of treating wood with'an organic solventsolublefire retardant in a solutionof an organophosphorus solute in an organic solution without altering the dimensions of thewood, comprising the steps of: I V

a (a) impregnating the wood under wood impregnating pressure at a temperature belowthe boiling point of said solvent undersaid pressure, with said solution consisting essentially ofYsaid solute selected from the group consisting of trimethyl phosphite, and a compound having the formula:

. I (R nr x, wherein R is a member selected from the group consisting of lower alkyl radicals and chlorinated lower alkyls, X is a hydroxy radical, and n is an in- "teger having a value of from one to two, and said solvent having a boiling point below about C. U and selected from the group consisting of methylene chloride, chloroform,.oarbon tetrachloride, ether, benzene and pentane, and mixtures thereof with low boiling alkanes V .'(b) evaporating'said solvent, whereby between} percent to wood,

(c) 'treating theimpregnated wood containing atleast a. four percentmoisture with an excess of gaseous am ZOpercentof the solute is retained by the l 5' e monia under wood impregnating pressure whereby 6. Method according to claim 1, wherein the solute is the ammonium salts are produced in situ, bis{beta-ch1oroethy1) phosphate. (d) removing the excess unreacted ammonia by difv 7. Method according to claim 1, wherein the solute is fusion from the wood at a pressure ranging between bis(1,3-dich1oropropy1)phosphite. atmospheric and sub-atmospheric pressure. 5 I 2. Method according to claim 1, wherein the organic Referemcs Cited by me Exammer solution consists of from 10 to 25 percent of trirnethyl UNITED STATES PATENTS phosphite in a penta-ne SOIVEIII. 2 3. Method according to claim 1, wherein the solute is 2678330 5/54 sizi g 1%;;g t-5 5 2 dunethyl PhosPhlte- 10 2,772,188 11/56 Reeves et a1. 117-135 4. Method according to claim 1, wherem the solute is 2,868 673 1/59 Depew et aL 117 147 XR I diethyl phosphate. 1

5. Method according to claim 1, wherein the solute is WQJLIAM MARTIN, Primary Examine!- dlethyl p pthte. RICHARD D. NEVIUS, Examiner. 

1. A METHOD OF TREATING WOOD WITH ANORGANIC SOLVENTSOLUBLE FIRE RETARDANT IN A SOLUTION OF AN ORGANOPHOSPHORUS SOLUTE IN AN ORGANIC SOLUTION WITHOUT ALTERING THE DIMENSIONS OF THE WOOD, COMPRISING THE STEPS OF: (A) IMPREGNATING THE WOOD, UNDER WOOD IMPREGNATING PRESSURE AT A TEMPERATURE BELOW THE BOILING POINT OF SAID SOLVENT UNDER SAID PRESSURE, WITH SAID SOLUTION CONSISTING ESSENTIALLY OF SAID SOLUTE SELECTED FROM THE GROUP CONSISTING OF TRIMETHYL PHOSPHITE, AND A COMPOUND HAVING THE FORMULA: 